Darel Hunting

Specificity of adenosine deaminase inhibitors.

Abstract The specificity of the potent adenosine deaminase inhibitors deoxycoformycin (covidarabine), coformycin and erythro -9-(2-hydroxy-3-nonyl)adenine (EHNA), has been assessed in Ehrlich ascites tumor cells in vitro and in cultured mouse lymphoma L5178Y cells. EHNA is both less potent an inhibitor of adenosine deaminase than deoxycoformycin, and is less specific. High concentrations of deoxycoformycin and EHNA inhibit all pathways of purine ribonucleotide synthesis, and inhibit the conversion of inosinate to adenine and guanine nucleotides. These drugs also inhibit purified adenylate deaminase, but inhibition of this enzyme in intact cells can only be detected at high rates of deamination of adenylate. Deoxycoformycin potentiates the toxicity of adenine against cultured cells.

Effects of 6-aminonicotinamide on cell growth, poly(ADP-ribose) synthesis and nucleotide metabolism

The purpose of this study was to determine if the cytotoxic effects of 6-aminonicotinamide are solely the result of an inhibition of poly(ADP-ribose) synthesis. The effects of 6-aminonicotinamide on cell growth, poly(ADP-ribose) synthesis and nucleotide concentrations were compared with the effect of 3-aminobenzamide, a more potent inhibitor of poly(ADP-ribose) synthesis. The growth of L1210 cells was not inhibited by 1 mM 3-aminobenzamide and was only slightly inhibited by 5 mM 3-aminobenzamide even though poly(ADP-ribose) synthesis, as measured by the N-methyl N-nitrosourea induced depletion of NAD+, was inhibited substantially. In contrast, 6-aminonicotinamide was found to be a potent inhibitor of L1210 and CHO cell growth. A 5 mM concentration of 3-aminobenzamide had no effect on purine and pyrimidine ribonucleotide concentrations or on the ATP to ADP ratio, but it did cause a slight elevation of NAD+. 6-Aminonicotinamide at 0.01 mM caused a depletion of purine and pyrimidine nucleotides and NAD+ as well as a reduction in the ATP to ADP ratio. 6-Aminonicotinamide at 1 mM caused a substantial inhibition of purine nucleotide synthesis from [14C] glycine but did not stimulate ATP breakdown. We conclude that inhibition of poly(ADP-ribose) synthesis caused little growth inhibition in itself and that the effects of 6-amininicotinamide on nucleotide metabolism were sufficient to produce an inhibition of both cell growth and DNA repair.

Relationship between ribo- and deoxyribonucleotide concentrations and biological parameters in cultured chinese hamster ovary cells☆

The relationship between ribo- and deoxyribonucleotide concentrations, growth rate and cell visibility has been studied. Nucleotide pools were manipulated using mycophenolic acid, pyrazofurin, phosphonoacetyl-L-aspartate (PALA) or thymidine. Growth rate, cell viability, nigrosin exclusion, progression through the cell cycle, and the rates of nucleic acid synthesis were measured. The observed qualitative relationships between nucleotide concentrations and growth rate can be rationalized in terms of the effects of changes in substrate availability on nucleic acid synthesis. However, there is no discernible relationship between changes in nucleotide concentrations and the loss of cell viability. More detailed studies will be required to elucidate each step in the complex process leading from the initial changes in nucleotide concentrations to cell death.